It is hard to monetize an open source project. Giving GPL/LGPL license for free and then charging for commercial license may work to some extent, but not for all. Many software engineers have a mindset that if something is open source, then they can take the code and incorporate it into their software regardless of licensing issues. They simply don’t bother reading and understanding the LGPL license. And even if they did, what would you do if you find that the framework is used in the way which violates the license? Nothing, if you are not a big company with lawyers working for you.

Another option would be to charge for requested features. There are some issues again. Many people don’t get complexity of their requests in computer vision area, so they step back as soon as you do some rough estimations. Plus it may be hard to estimate in the first place, since it is heavily based on R&D.

Also it is hard to make transition from hobby project to a start-up for an open source project. There is no support/funds behind the project, so you cannot spend full time on it. But having it as a second job for free may not be so encouraging. It is OK for a couple of years, but when you spend 6 years on it and find that your hobby interests are not always equal to what users want from you (but don’t reward you for), then it all changes.